(1) Field of the Invention
The present invention relates to a water-in-oil emulsion explosive composition (hereinafter, abbreviated as W/O emulsion explosive composition), and more particularly relates to a W/O emulsion explosive composition containing a novel emulsifier, which can form W/O emulsion, and having a performance superior to conventional W/O emulsion explosive compositions containing a commonly known emulsifier in the storage stability in the detonation sensitivity in a small diameter cartridge (diameter: 25 mm) and at low temperature.
(2) Description of the Prior Art
There have been variously investigated W/O emulsion explosive compositions for a long period of time. However, W/O emulsion explosive compositions produced in the early stage investigation are unstable in their emulsion state (that is, the contact area of the disperse phase and the continuous phase is relatively small), and therefore in almost all of the initial stage W/O emulsion explosive compositions, their detonation sensitivity in a small diameter cartridge was improved by compounding thereto an explosive sensitizer, such as nitroglycerine or the like, or a nonexplosive sensitizer, such as monomethylamine nitrate or the like (hereinafter these explosive sensitizer and nonexplosive sensitizer are referred to as sensitive substances), a detonation-catalytic sensitizer, such as a compound of metals having an atomic number of at least 13 and being other than the metals of Groups I and II in the Periodic Table, a strontium compound or the like, or a sensitive oxidizer, such as perchlorate or the like of ammonium or alkali metals (hereinafter, these detonation-catalytic sensitizer and sensitive oxidizer are referred to as auxiliary sensitive substances). However, W/O emulsion explosive compositions containing the above described sensitive substance or auxiliary sensitive substance have the dangerous property that, when the sensitive substance or auxiliary sensitive substance is separated at the production of the W/O emulsion explosive composition or during the use thereof, the explosive composition becomes very sensitive, or the toxic property of the sensitive or auxiliary sensitive substance appears. In order to obviate these drawbacks, there have been proposed W/O emulsion explosive compositions having an improved detonation sensitivity in a small diameter cartridge (capable of being detonated by a blasting cap) without containing any of the above described sensitive substances and auxiliary sensitive substances.
For example, U.S. Pat. No. 4,110,134 discloses that W/O emulsion explosive compositions, which contain an emulisifier of sorbitan fatty acid ester, glycerine fatty acid ester, polyoxyethylene sorbitol fatty acid ester, polyoxyethylene ether, polyoxyalkylene oleic acid ester, polyoxyalkylene lauric acid ester, phosphoric acid oleic acid ester, substituted oxazoline or phosphoric acid ester and which further contain a gas-retaining agent of glass microballoon, can be completely detonated up to a density of maximum 1.25 in a cartridge diameter of about 1.25 inches (31.8 mm) by means of a No. 6 blasting cap.
U.S. Pat. No. 4,149,917 discloses that W/O emulsion explosive compositions, which contain an emulsifier of sorbitan fatty acid ester, glycerine fatty acid ester, polyoxyethylene sorbitol fatty acid ester, polyoxyethylene(4) lauryl ether, polyoxyethylene(2) ether, polyoxyethylene(2) stearyl ether, polyoxyalkylene oleic acid ester, polyoxyalkylene lauric acid ester, phosphoric acid oleic acid ester, substituted oxazoline, phosphoric acid ester or their mixture and whose density has been adjusted to 0.95 by microbubbles without the use of a gas-retaining agent can be completely detonated (explosive temperature: 21.1.degree. C.) in a cartridge diameter of 1.25 inches (31.8 mm) by means of a No. 6 blastic cap even after the lapse of time of 2 months and by means of a No. 8 blasting cap even after the lapse of time of 8 months after the production of the explosive composition.
Therefore, it is commonly known that various emulsifiers are used in a W/O emulsion explosive composition not containing the above described sensitive substance or auxiliary sensitive substance. Further, there are known various emulsifiers capable of forming W/O emulsion. However, W/O emulsion explosive compositions using an emulsifier other than that disclosed in the above described U.S. patents use the above described sensitive substance or auxiliary sensitive substance. This fact shows that the W/O emulsion is poor in storage stability, and the W/O emulsion explosive composition is very poor in storage stability in detonation sensitivity in a small diameter cartridge (diameter: 25 mm) and at low temperature.
The W/O emulsion explosive composition using the emulsifier described in the above described U.S. patents are still insufficient in storage stability in detonation sensitivity in a small diameter cartridge (diameter: 25 mm) and at low temperature.
The inventors have made various investigations for a long period of time in order to solve the above described problems, and found out that an aqueous solution consisting of water and ammonium nitrate, or a mixture of ammonium nitrate and the other oxidizer salt, and a combustible material consisting of fuel oil/wax can be formed into a W/O emulsion by the use of a compound which has not hitherto been considered as an emulsifier for W/O emulsion explosive composition; and further found out that the resulting W/O emulsion explosive composition is superior to W/O emulsion explosive compositions containing a commonly known emulsifier in storage stability in detonation sensitivity in a small diameter cartridge and at low temperature. As a result, the present invention has been accomplished.